A liquid crystal element is small in size and has high durability since it has no moving element, and has been thereby attracted attention for an optical modulation element. For example, its use as a laser beam modulation element as mounted on an optical head device has been proposed (for example, Patent Documents 1 and 2). In recent years, for the purpose of improving the recording density, blue shift of the laser beam to be used for reading and writing on an optical disk is in progress, and development of a high density optical disk which employs a laser beam having a wavelength of at most 500 nm (a wavelength in the vicinity of 405 nm for example) for reading and writing is in progress. Accordingly, a liquid crystal element to modulate a laser beam in this wavelength region is required (for example, Non Patent Document 1).
A liquid crystal element used for such an application is usually one having a layer of a liquid crystal composition sandwiched between a pair of transparent substrates facing each other, and each of the pair of transparent substrates has an electrode and an alignment film comprising a polyimide laminated in this order on the surface which faces the other transparent substrate, and the alignment film and the liquid crystal composition are in contact with each other. This alignment film is usually subjected to rubbing treatment, and liquid crystals in contact with one another in the liquid crystal composition are aligned in the rubbing direction with an angle of from several degrees to about ten degrees with the surface to which the alignment film is applied (hereinafter this angle will be referred to as the “pretilt angle”). As a material of the alignment film, a polyimide, which has high heat resistance and insulating properties, has been widely used.    Patent Document 1: JP-A-2002-260269    Patent Document 2: JP-A-2002-237077    Non Patent Document 1: “2002 International Symposium on Optical Memory and Optical Data Storage Topical Meeting Technical Digest” p. 57